Genzyme Corp. reported on Oct. 14th that data from a phase II trial of its biologic drug alemtuzumab, sold as Campath in the U.S. for treatment of leukemia, showed the biologic to be very effective in treating multiple sclerosis, but said patients must be monitored to avoid a potentially deadly side effect.

Results from the trial involving 334 patients with multiple sclerosis, presented at the Congress of the European Committee for Treatment and Research in Multiple Sclerosis in Prague, showed that alemtuzumab reduced risk of relapse by 70 percent compared to patients taking biologic Merck Serono's Rebif.

"These results demonstrate the durability of the previously reported effect of alemtuzumab for the treatment of multiple sclerosis that, by our analysis, exceeds any marketed products and anything that we can see in development," said Dr. Richard Moscicki, Genzyme chief medical officer.

But to protect against side effects seen in the three-years of the trial which include a decline in platelet counts that can lead to potentially catastrophic internal bleeding, Genzyme said patients must have their blood drawn once a month so that any decline in platelet count can be treated and reversed.

Genzyme said it has initiated Phase III studies testing alemtuzumab against Rebif, and hopes to file for regulatory approval to market the biologic for treatment of multiple sclerosis in 2010 or 2011.

Alemtuzumab is a monoclonal antibody which targets CD52, a protein present on the surface of mature llymphocytes, but not on the stem cells from which these lymphocytes were derived.